Re: BVI chart/nav app
"Line of sight" sailing generally applies in the BVI, but not if you are going to Anegada. Coming back from Anegada is a different matter.
I've also been caught in the Drake Channel in an intense rain event where the visibility was down to a quarter mile. These events don't last long, thankfully, so we recovered visual landmarks after a while. I didn't have GPS then, but it would have been nice.
The GPS allows you to navigate precisely to a harbor entrance that otherwise blends into the background. It's true that visual navigation will usually keep you out of trouble, but GPS can be a convenience.
Then there are those of us who are used to dead reckoning in areas that have tidal currents and are quite capable of navigating with a compass and a paper chart, but still want to know precisely where we and the waypoint are at all times.